Fractional Change In Resistance Research Articles

Role of Carbon Nanofiber on the Electrical Resistivity of Mortar under Compressive Load

A nanomodified cement consisting of particles with in situ synthesized carbon nanofibers was developed to introduce a strong load-sensing capability of the hydrated binder matrix. The material was produced using chemical vapor deposition. The nanomodified cement contained 2.71 wt% of carbon nanofibers (CNFs). The electrical properties of the composite were determined. Several mortar samples were prepared by partially substituting ordinary Portland cement with 2, 4, 6, 8, and 10 wt% of the nanomodified cement. Additionally an ordinary Portland cement mortar was used as reference. The results show that the strongest piezoresistive response and therefore the best load-sensing was obtained for the mortar containing the highest amount of CNFs. This mortar contained 10 wt% of nanomodified cement. The fractional change in electrical resistivity of this mortar was 82% and this mortar had a compressive strength of 28 MPa.

Effect of micro-cracking on the electrical and self-sensing properties of an engineered cementitious composite under tensile straining

The piezo-resistive response of a relatively mature engineered cementitious composite (ECC) under tensile straining is investigated and compared with previous studies. In this work, tensile tests were performed on four dog-bone shaped ECC samples and during the loading process, electrical impedance measurements were undertaken over the frequency range 100Hz-1MHz to identify the bulk resistance (hence accurate evaluation of resistivity). At the same time, digital images of the front face of the dog-bone samples were recorded throughout the entire loading process to enable detailed crack width analysis to be taken after testing and to monitor micro-crack formation during testing, using the digital image correlation. It is shown that tensile straining resulted in an overall increase in impedance, but retained a similar overall profile with a weakly developed spur evident at the low-frequency side of the impedance spectrum and a circular arc at the high-frequency side. It is also shown that the fractional change in resistivity increases nonlinearly with strain and is related to the nature of micro-crack formation. Published values for fractional change in resistivity and its relation with strain were found to be in a large scatter and in this study, attention is therefore focused on the crack width distribution during loading.

A critical review of piezoresistivity and its application in electrical-resistance-based strain sensing

Piezoresistivity is an electromechanical effect characterized by the reversible change in the electrical resistivity with strain. It is useful for electrical-resistance-based strain/stress sensing. The resistivity can be the volumetric, interfacial or surface resistivity, though the volumetric resistivity is most meaningful scientifically. Because the irreversible resistivity change (due to damage or an irreversible microstructural change) adds to the reversible change that occurs at lower strains, the inclusion of the irreversible effect makes the piezoresistivity appear stronger than the inherent effect. This paper focuses on the inherent piezoresistivity that occurs without irreversible resistivity changes. The effect is described by the gage factor (GF), which is defined as the fractional change in resistance per unit strain. The GF can be positive or negative. Strong piezoresistivity involves the magnitude of the fractional change in resistivity much exceeding the strain magnitude. The reversible effect of strain on the electrical connectivity is the primary piezoresistivity mechanism. Giant piezoresistivity is characterized by GF ≥ 500. This critical review with 209 references covers the theory, mechanisms, methodology and status of piezoresistivity, and provides the first review of the emerging field of giant piezoresistivity. Piezoresistivity is exhibited by electrically conductive materials, particularly metals, carbons and composite materials with conductive fillers and nonconductive matrices. They include functional and structural materials. Piezoresistivity enables structural materials to be self-sensing. Unfortunately, GF was incorrectly or unreliably reported in a substantial fraction of the publications, due to the pitfalls systematically presented here. The most common pitfall involves using the two-probe method for the resistance measurement.

Electrical resistivity and piezoresistivity of cement mortar containing ground granulated blast furnace slag

Ground granulated blast furnace slag (GGBFS) is a popular used supplementary cementitious material which can increase the resistivity of cement-based composites, contribute to the cement hydration, and dense the composite structure. The piezoresistivity of cement mortar containing GGBFS was studied in this paper. Three GGBFS/cement ratio, 1.2, 1.5, and 1.8, were designed to study the effect of GGBFS content on the piezoresistivity behaviour of cement mortar. Samples were measured before and after drying treatment, and three water/binder ratios were designed to study the influence of water content on the electrical properties. Furthermore, mechanical properties and microscopy analysis were conducted. Results showed that compared to pure cement mortar, samples containing GGBFS showed an improvement in piezoresistivity behaviour. Sample with GGBFS/cement ratio at 1.2 performed the largest fractional change in resistivity of 5.57, 9.23 and 16.73 with water/binder ratio at 0.3, 0.4 and 0.5, respectively, as the concentration of pore solution was higher for samples with GGBFS/cement ratio at 1.2 compared to pure cement mortar. However, with the increasing GGBFS/cement ratio, the piezoresistivity performance was adversely affected due to the reduced pore solution concentration and conductivity caused by the increasing assumption of free calcium hydroxide. Through the investigation, piezoresistivity performance of the cement-based composite was found to be related to the mobile ions transportation with the pore solution.

Model-based evaluation of the microhemodynamic effects of PEGylated HBOC molecules in the rat brain cortex: a laser speckle imaging study

Hemoglobin-based oxygen carriers (HBOCs) were developed with the aim of substituting transfusions in emergency events. However, they exhibit adverse events, such as nitric oxide (NO) scavenging, vasoactivity, enhanced platelet aggregation, presently hampering their clinical application. The impact of two prototypical PEGylated HBOCs, Euro-PEG-Hb and PEG-HbO2, endowed by different oxygen affinities and hydrodynamic volumes, was assessed on the cerebrocortical parenchymal microhemodynamics, and extravasation through the blood-brain-barrier (BBB) by laser speckle contrast imaging (LSCI) method and near-infrared (NIR) imaging, respectively. By evaluating voxel-wise cerebrocortical red blood cell velocity, non-invasively for its mean kernel-wise value ( ), and model-derived kernel-wise predictions for microregional tissue hematocrit, THt, and fractional change in hematocrit-corrected vascular resistance, R', as measures of potential adverse effects (enhanced platelet aggregation and vasoactivity, respectively) we found i) no significant difference between tested HBOCs in the systemic and microregional parameters, and in the relative spatial dispersion of THt, and R' as additional measures of HBOC-related adverse effects, and ii) no extravasation through BBB by Euro-PEG-Hb. We conclude that Euro-PEG-Hb does not exhibit adverse effects in the brain microcirculation that could be directly attributed to NO scavenging.

Effects of Steelmaking Slag and Moisture on Electrical Properties of Concrete.

Strain sensors can indicate the conditions of concrete structures, but these sensors are only capable of measuring local behaviors of materials. To solve this problem, researchers have introduced conductive materials that can monitor the overall behavior of concrete structures. Steelmaking slag, which contains large amounts of iron oxide (Fe2O3), is conductive, and researchers have considered the addition of this material to improve concrete monitoring. In this study, mechanical and electrical properties of concrete containing steelmaking slag as a binder were evaluated. As the incorporation of steelmaking slag increased, the setting times were delayed, but the compressive strengths were similar within the replacement ratio of 15%. It was found that the addition of steelmaking slag with Fe2O3, the main ingredient of magnetite (Fe3O4), improved the electrical resistivity, piezoresistivity, and sensitivity of the concrete. Drying of the concretes resulted in an increase in electrical resistance and fractional change in resistivity (FCR). Expansion of steelmaking slag, due to contacting of free CaO and moisture under repeated loads, resulted in cracks in the concrete and affected the gauge factor (GF). This study demonstrates the possibility that the addition of steelmaking slag as a binder may provide an economical and environmentally-friendly solution to concrete strain monitoring.

Influence of electrode configuration on impact damage evaluation of self-sensing hierarchical composites

A technique based on the electrical resistance change of a network of carbon nanotubes within a polymer composite was implemented to assess damage caused by low-velocity impact in multiscale hierarchical composites. The influence of the electrode configuration in 100 mm x 100 mm x 1.7 mm plates is addressed. Three electrode configurations are evaluated, namely, a grid on the impacted surface, a grid on the opposite (non-impacted) surface, and through the thickness of the plate. Upon impact, matrix cracking, delamination, and fiber rupture cause disruption and redistribution of the electrical network of carbon nanotubes, whose electrical resistance changes can be correlated with such damage. It is found that the non-impacted surface exhibits a higher fractional change of electrical resistance and hence higher sensitivity to damage. The results obtained using the electrical technique showed a good correlation with damage detected by independent measurements by digital holographic interferometry and ultrasonic inspections.

Tailoring sensing properties of smart cementitious composites based on excluded volume theory and electrostatic self-assembly

The excluded volume effect is the reduction in free volume of a matrix filled by secondary fillers, which can enhance the conductive network of carbon nanotubes (CNTs) composites and work effectively with microscale secondary fillers. Besides, the electrostatic self-assembly method has been proved effective for dispersing CNTs. Therefore, this study aims to assemble microscale TiO2 with CNTs to develop smart cementitious composites, in an effort to tailor the sensing properties based on the excluded volume theory and electrostatic self-assembly method. The results show the composites with CNT/TiO2 have a high sensitivity, a wide stress/strain monitoring range, and acceptable mechanical properties. In elastic state, the strain sensitivity of cementitious composites can reach 317. The composite can monitor the compressive stress from 0 to 80.7 MPa, with the maximum fractional change in resistivity as high as 84.09%. Furthermore, due to its low water absorption property, the CNT/TiO2 filler exhibits little negative effect on the mechanical properties of cementitious materials with best piezoelectric performance.

Effects of steel slag aggregate size and content on piezoresistive responses of smart ultra-high-performance fiber-reinforced concretes

This study investigated the self-sensing characteristics of smart ultra-high-performance concretes (UHPCs) containing steel slag aggregates (SSAs) and steel fibers under compression. We used SSAs as functional fillers in smart UHPCs, instead of silica sands, to obtain a uniform filler distribution. We examined the effects of SSA particle size (0.39, 2, and 5 mm in max. diameter), SSA/cement ratio (SSA/C) by weight (0.5, 1, 1.5, and 2), and steel fiber content (1 and 2 vol%) on the piezoresistive response of smart UHPCs. The smart UHPC containing SSAs with a maximum diameter of 0.39 mm and a SSA/C of 0.5 and a steel fiber content of 2 vol% produced the highest fractional change in resistance (FCR = 42.9 %) and consequently the highest stress sensitive coefficient (FCR/σ = 0.298 %/MPa) under compression owing to a well-structured conductive network of functional fillers (SSAs and fibers). Coarser SSA size generated non-uniform distribution of steel fibers while high volume contents of SSA incorporating with steel fibers consequently resulted in low piezoresistive responses by exceeding the percolation threshold of functional fillers in smart UHPCs.

Synthesis, design and piezo-resistive characteristics of cementitious smart nanocomposites with different types of functionalized MWCNTs under long cyclic loading

In recent years, carbon nanotubes (CNTs) incorporated smart cement composites have attracted significant attention as it opens up a new avenue to develop new class of sensors, in general, and uniquely enables the structural materials to reflect the internal stress state, in particular. However, dispersion of CNTs, threshold limit, polarization effect, type and design of electrode, effect of functionalization of CNTs etc. on piezo-resistive properties of cementitious nanocomposites need further investigations. The present study describes the systematic approach for developing cement based smart nanocomposites exploiting the unique capabilities of functionalized MWCNTs and comprehensive studies on performance under monotonic- and long reverse cyclic-loading. Three different types of multiwalled carbon nanotubes (MWCNTs) like pristine MWCNTs, hydroxyl (-OH) MWCNTs and carboxyl acid (-COOH) MWCNTs are considered. The response of cement based smart nanocomposites under cyclic compression load was measured in terms of fractional change in resistivity (FCR) where type and dosage of CNT, type of electrode are the parameters. The test results indicate that the performance of the smart composite with COOH-MWCNTs is superior compared to other types and the gauge factor of the composite is found to be as high as 451. The study also emphasizes the role of stabilization, tunneling effects and formation of conductive paths in imparting the piezo-resistive properties in porous, nonconductive materials like cement composites.

Piezoelectret-based and piezoresistivity-based stress self-sensing in steel beams under flexure

This work reports for the first time the structural self-sensing of stress in steel beams under flexure (elastic regime, ≤200 MPa) through measurement of the electric field (piezoelectret), capacitance (dielectricity) and resistance (piezoresistivity). Coplanar electrodes on the top or bottom surface are used. Under flexure, the electric field and resistance increase at the top surface, but decrease at the bottom surface, while the capacitance decreases at both surfaces. Under normal compression, the electric field, capacitance and resistance decrease at both surfaces. For flexure and normal compression, the resistance and capacitance changes are essentially completely reversible, whereas the electric field change is not. Longitudinal tension (whether in flexure or normal compression) causes the electric field to decrease, whereas longitudinal compression (in flexure) causes the electric field to increase. Longitudinal tension (whether in flexure or normal compression) causes the resistance to decrease, whereas longitudinal compression (in flexure) causes the resistance to increase (negative piezoresistivity). The capacitance (2 kHz) decreases due to the stress (whether flexure or normal compression and whether at the top or bottom surface) and is attributed to the permittivity decrease, except that the capacitance decrease under longitudinal compression (in flexure) is attributed to the AC voltage used to measure the capacitance penetrating the full thickness and the effect of longitudinal tension at the bottom surface dominating over that of longitudinal compression at the top surface. In contrast, the DC voltage used to measure the resistance is much smaller and does not penetrate the full thickness, so that the resistances at the top and bottom surfaces respond to flexure differently. The magnitude of the fractional change in electric field, capacitance or resistance increases with decreasing beam width.

Strain and Damage Sensing Property of Self-compacting Concrete Reinforced with Carbon Fibers

Present paper investigated the strain and damage sensing property on concrete cubes embedded with carbon fibers. Concrete cubes of dimension 150 mm have been casted with different concentration of carbon fibers to study the strain and damage sensing property under cyclic loading that can be further used for health monitoring as non-destructive testing (NDT) approach. All the specimens were tested under cyclic loading within elastic region of the sample for three cycles of loading with a maximum load of 195kN for strain sensing test. During cyclic loading, fractional change in resistance (FCR) is calculated and co-relation with the stress is plotted. During strain sensing test, gauge factors (GF) were also calculated during loading and unloading on the samples. From obtained results, it is found that the concrete sample containing 1.5% of carbon fibers by weight of cement gives best co-relation between stress and FCR that can be further used for health monitoring purpose. Along with strain sensing property, damage sensing property and ultimate load carrying capacities of all the specimens are also reported in present paper with detailed explanation.

Mechanical and Strain-Sensing Properties of Cement-Matrix Composite Containing Nano-Sized Carbon Black

An experimental researches was performed for carbon black-reinforced cement-matrix composites. The carbon black used was in the form of particles with a nano-size. Results show that when content of the carbon black is between 0.25% and 0.75% by weight of cement, both flexural and compressive strengths of the composite can be enhanced. Flexural strength increases up to 9.69%, and compressive strength increases up to 6.92%, respectively. Moreover, the carbon black-reinforced composite is of high strain-sensing ability. The fractional change in resistance () increases monotonically upon compressive loading, and decreases monotonically upon unloading. These properties indicate that the carbon black-reinforced composite can be used for structural function, while at the same time act as a strain sensor itself. Compared with carbon fiber-reinforced composites, the carbon black-reinforced composite has a low price and is easy for mixing.

Study on self-monitoring of multiple cracked concrete beams with multiphase conductive materials subjected to bending

The multiphasic conductive admixtures like macro steel fiber (SF), nano carbon black (NCB) and carbon fiber (CF) are incorporated into concrete to improve the conductivity and mechanical properties. In this study, the mechanical and conductive properties of the concrete beam are explored by the hybrid use of different conductive admixtures. The deflection hardening (multiple cracking) behavior of concrete beam with different fiber content, monitoring of single and multiple cracks of diphasic (SF+NCB) and triphasic (SF+CF+NCB) conductive concrete beam through resistance measurement is investigated. Moreover, the relationship between fractional change in resistance (FCR) and crack opening displacement is established to study the influence of different types and amounts of electric conductive admixtures on self-sensing behavior of concrete beam. Results reveal that the deflection hardening (multiple cracking) behavior is obtained with 70 kg m−3 SF content. The single and multiple cracks monitoring is illustrated through load-time and FCR-time relationship. In addition, FCR improved linearly with an increment of NCB with triphasic conductive admixtures.

Mechanical and self-monitoring behaviors of 3D printing smart continuous carbon fiber-thermoplastic lattice truss sandwich structure

A novel method for manufacturing smart continuous carbon fiber (CCF)-thermoplastic lattice truss sandwich structures (LTSSs) is presented in this study, combining the conventional fused deposition modeling (FDM) technique and the free-hanging three-dimensional (3D) printing technique. Self-monitoring of LTSSs is achieved by measuring the fractional change in electrical resistance (ΔR/R0) of the LTSSs. Monotonic out-of-plane compression test and cyclic loading test are carried out to investigate the mechanical properties, failure modes and self-monitoring capacity of the printed LTSSs. Results show that the LTSSs with truss inclination angle of 50° have an optimal compressive strength with a value of 1.236 ± 0.063 MPa, while LTSSs with truss inclination angle of 60° have an optimal compressive modulus with a value of 17.134 ± 1.92 MPa. A bilinear relationship between ΔR/R0 and stain during the whole loading process is observed, indicating that ΔR/R0 can be used to sense the compressive strain, stress and predict the damage. Matrix fracture, Euler buckling, as well as carbon fiber debonding are found within damaged LTSSs using X-ray tomography. Generally, the results indicate that the LTSSs have superior mechanical properties and self-monitoring capacity, which can help to promote the smart LTSSs applications in many engineering fields, such as aerospace and automotive industry.

Mechanical and Self-Sensing Properties of Multiwalled Carbon Nanotube-Reinforced ECCs

This paper investigates the effect of type and dosage of multiwalled carbon nanotubes (MWCNTs) on the mechanical and self-sensing properties of engineered cementitious composites (ECCs). Two types of MWCNTs (MWCNTa and MWCNTb) were employed. The tensile and flexural strengths of CNT-reinforced ECCs were improved compared with normal ECCs, while the ultimate tensile strain and midspan deflection were reduced. Compared with the dosage of MWCNTs, the type had less effect on these properties. The percolation threshold was around 0.3 wt.%. ECCs containing MWCNTs had good self-sensing ability under different loading conditions. When the midspan deflection increased from 0.1 to 0.6 mm, the fractional change in resistivity reached 9%. The dosage of MWCNTs had a significant effect on the self-sensing ability. As the MWCNT content increased, the amplitude of fractional change in resistivity decreased.

Effect of Temperature on Resistivity of CFRP Materials with Added Carbon Powder or Nano-silica

This paper presents an experimental investigation on the effect of temperature on resistivity of Carbon Fiber Reinforced Polymer (CFRP) materials. A series of tests were conducted on three types of CFRP materials, namely pure CFRP material, CFRP with carbon powder (4% in weight) and CFRP with nano-silica (4% in weight). Test results showed that adding carbon powder into the epoxy resin decreases the initial electric resistance R0 and initial volume resistivity ρ0 while adding nano-silica increases R0 and ρ0 compared to pure CFRP material. Preheating cycle test results showed that the volume resistivity of all three types of specimens linearly increases with increasing temperature. CFRP with added nano-silica exhibits higher temperature sensitivity than CFRP with added carbon powder compared to the lowest temperature sensitivity for pure CFRP material. In addition, temperature cycle test results showed that CFRP specimens have approximately stable values of volume resistivity. Both CFRP specimens with added carbon powder or nano-silica exhibit a recognizable trend of first decrease and then increase in volume resistivity with increasing temperature both during heating and cooling cycles. CFRP with added carbon powder mainly shows Negative Temperature Coefficient (NTC) effect in the temperature range of −40 to 40°C and Positive Temperature Coefficient (PTC) effect from 40 to 80°C. CFRP with added nano-silica mainly exhibits PTC effect in the temperature domain of −15 to 80°C and NTC effect from −40 to −15°C. A mathematical-physical model with respect to the thermal effect was presented based on the Eshelby-Mori-Tanaka (EMT) approach and mesomechanics method. The results obtained with the model agree well with the test results considering the temperature domain of PTC effect, which indicates that the proposed model is effective in characterizing the variation of fractional change in resistance (ΔR/R0) at varying temperature.

Piezoelectricity, piezoresistivity and dielectricity discovered in solder

The performance and reliability of soldered joints are important for electronic packaging. This work provides the first observation of piezoelectricity (generating electric field and capacitance), piezoresistivity (changing the resistivity) and dielectricity (giving polarization) in solder. These effects influence electrical conduction. The solder may encounter stress (particularly thermal stress) during use in a soldered joint. The solder studied is the tin–lead eutectic alloy. The stress is tensile in the direction of electrical measurement. Although the piezoelectric coupling coefficient d33 of the solder (− (7.5 ± 0.8) × 10−6 pC/N) is very low compared to those of the well-known piezoelectric materials, the resulting electric field and capacitance are substantial and the changes are reversible upon unloading. The relative permittivity (2 kHz) (a dielectric material property) is very high ((3.973 ± 0.017) × 106) compared to those of conventional dielectric materials, but is comparable to those of previously reported steels. The polarization is due to the movement of the free electrons; it opposes the applied electric field. The permittivity increases reversibly with increasing tensile stress and is attributed to an unidentified reversible microstructural change. The permittivity increase contributes to d33 by only + (4.3 ± 0.6) × 10−7 pC/N, which is opposite in sign from the abovementioned overall negative d. The gage factor (fractional change in resistance per unit strain) associated with piezoresistivity is high (85 ± 6). The resistivity increases substantially and reversibly with increasing stress; it is attributed to the microstructural change and is disadvantageous for electrical conduction. However, the piezoelectricity and piezoresistivity enable the solder to sense its own condition (stress) without embedded or attached sensors.

Effect of water content on the piezoresistive property of smart cement-based materials with carbon nanotube/nanocarbon black composite filler

A carbon nanotube (CNT)/nanocarbon black (NCB) composite filler was incorporated into cement matrix to develop smart cement-based materials with piezoresistive property. However, the effect of water on the cement-based materials with CNT/NCB composite filler is not easy to avoid in practical engineering. Therefore, in this paper, the effect and mechanisms of water content on the piezoresistive property of cement-based materials with CNT/NCB composite filler are investigated. Cement-based materials with fillers feature the piezoresistive property under different water contents. However, the maximum fractional changes in electrical resistivity, stress sensitivity and strain sensitivity all decrease with the reduction in water content. The maximum values of fractional change in electrical resistivity, stress sensitivity and strain sensitivity of the cement-based material with 2.14 vol% of filler change nonlinearly from −12.94% to −6.80%, 3.15%/MPa to 1.70%/MPa, and 389 to 202, respectively, with decreasing water content. With the reduction in water content, the decrease in contact resistance between fillers and the increase in the composite shrinkage result in a decrease in the sensitivity of the piezoresistive property.

Large-scale deformation and damage detection of 3D printed continuous carbon fiber reinforced polymer-matrix composite structures

For the efficient monitoring regional deformation and damage of continuous carbon fiber reinforced polymer-matrix composite structures, a dual-material three-dimensional printing process was developed, in which continuous carbon fiber tows were integrated within the polymer matrix to construct smart sensing grids. Strategies based on the electrical-mechanical behavior of continuous carbon fiber tow for locating loading position and recognizing deformation field distribution, as well as damage detection, have been presented. The loading location can be determined through the maximum fractional change in electrical resistance of continuous carbon fiber tows in the longitudinal and transverse direction. A model based on the electrical-mechanical behavior of carbon fiber tow has been developed to identify the deformation field distribution. Both micro-damage and macro-damage can be detected according to the dramatic change in the slope of fractional change in electrical resistance with the strain. The effectiveness of above methods has been verified through experiments.